ALL HOLDERS OF THE 5th EDITION
OF THE HIGHWAY DESIGN MANUAL
PROGRAM MANAGERS AND DIVISION CHIEFS FOR DESIGN, MAINTENANCE,
TRAFFIC & CONSTRUCTION

Date : March 30, 2000

File: 608-309.2

From:

DEPARTMENT OF TRANSPORTATIONDESIGN AND LOCAL PROGRAMS
MAIL STATION 28

Subject:

Vertical Clearances on the Rural and Single Interstate Routing
System

This memorandum supersedes the August 20, 1993 memorandum on
the 26,000 mile Priority Network (more recently termed the 42
000 km Priority Network). We are now issuing a revised map and
table describing the limits of the new rural and single interstate
routing system. The Department has received notification from
the Federal Highway Administration (FHWA) that the previously
established 42 000 km "Priority Network" is being eliminated,
based on an agreement between the FHWA and the Military Traffic
Management Command Transportation Engineering Agency (MTMCTEA).
The new requirement is that all rural and "Single Routing
Interstates" through urban areas will be required to meet
the 4.9 m vertical clearance standard over the entire roadway
width, including shoulders, as well as ramps and collector-distributor
roadways. Exceptions to the 4.9 m vertical clearance standard
will require approval by FHWA and the MTMCTEA. The Federal agencies
plan to select a name for the revised system in the immediate
future. Once a name has been selected, it will be included in
an update to the Highway Design Manual.

In coordination with MTMCTEA, the FHWA has identified a subset
of the Interstate System that would meet the most urgent national
defense needs. FHWA has committed to the MTMCTEA that a 4.9 m
minimum vertical clearance will be maintained where it already
exists and clearances of less than 4.9 m will be upgraded as rapidly
as practical. All projects on the rural and single interstate
routing system will be closely scrutinized to ensure compliance
with this vertical clearance standard. Exceptions to this standard,
regardless of funding, whether for new construction, a project
which creates a nonstandard situation, or for a project which
does not provide for the correction of existing nonstandard vertical
clearance (including 3R projects and CAPM), will be subject to
Federal review.

Current Caltrans practice for projects on the Interstate System
requires approval through the design exception fact sheet process
for any proposed vertical clearance of less than 5.1 m for new
construction or 4.9 m for overlay projects. Design exceptions
for clearances of less than 4.9 m on the rural and single Interstate
routing system must first receive internal review and approval
within Caltrans. If the exception is approved by the Project
Development Coordinator, the Project Engineer (PE) must submit
the completed Design Exception Fact Sheet, with appropriate signature
blocks, to the FHWA Division office. The transmittal must note
whether or not the fact sheet addresses additional nonstandard
design features on the proposed project. If the FHWA Division
office approves of the exception to vertical clearance standards,
FHWA will contact the MTMCTEA directly. The MTMCTEA has agreed
to a maximum 10-day turnaround in review and response to a vertical
clearance exception request. Due to this additional process,
potential requests for design exception must be identified as
early as possible and discussed with both the Project Development
Coordinator, from the office of Design and Local Programs, and
the FHWA.

For Interstate routes not on the rural and single Interstate
routing system, the PE shall complete the Design Exception Fact
sheet, submit to the Project Development Coordinator, and upon
PDC approval, notify both the FHWA Division office and the MTMCTEA
directly.

Wherever possible, vertical clearances should continue to be
designed to comply with the Caltrans standards as described in
the Highway Design Manual, Section 309.2. All exceptions to mandatory
design standards (including the same vertical clearance) shall
continue to require approval of a "Fact Sheet" as outlined
in Section 82.2 of the Highway Design Manual (HDM), and as described
in the Project Development Procedures Manual Chapter 21, format
found in Appendix BB. Once the final approval is obtained, the
Project Engineer shall send two copies of the approved Design
Exception to Design and Local Programs and file the original in
the project files.

Attached to this memo are two revised descriptions of the Interstate
routes within California. One is a tabular
description of the rural and single Interstate routing system,
and the other is a map providing
a quick general reference for both the rural and single Interstate
routings and other Interstate routes. These descriptions will
be included in the new HDM update as the revised HDM Table 309.2
and revised HDM Figure 309.2, respectively.

If you have any questions regarding this information, please
contact either the Project Development coordinator or the Design
Reviewer (formerly Geometric Reviewer) from the Office of Design
and Local Programs assigned to your District.

Original signed by:
ROBERT L. BUCKLEY
Program Manager
Design and Local Programs